1. Field of the Invention
This invention relates to mechanical drafting apparatus, and more particularly to an improved drafting apparatus for deriving an axonometric view of an object from two conventional perpendicular and normally aligned orthographic views of the object. More specifically, the axonometric view may be produced as a trimetric, dimetric or isometric view with its primary, secondary and tertiary surfaces oriented at nominal angles of five degree multiples with respect to non-converging lines of sight normal to the viewing plane of the axonometric view.
2. Brief Description of Prior Art
Various devices have been developed for producing axonometric views of an object from orthographic views of the object. Exemplary of such devices are those disclosed in U.S. Pat. Nos. 3,070,894, 3,157,951, 3,296,701 and 3,457,648.
Certain important considerations should be appreciated as they relate to drafting apparatus. Drafting apparatus which is prone to introduction of error is not desirable. Any drafting apparatus which is relatively complicated in construction and use, or which requires extensive familiarization, experience or knowledge of its use, may be prone to create situations where error is likely to occur, particularly with less experienced or less skillful use. These considerations are especially applicable to drafting apparatus for producing axonometric views of an object from its orthographic views. Another important consideration with respect to axonometric drafting apparatus is the ability to selectively produce dimetric, trimetric and isometric axonometric views of the object. Selective presentations of the various axonometric views is sometimes necessary to avoid hidden or superimposed details. Another important consideration is the ability to produce the axonometric view directly from the orthographic views, without reorienting the orthographic views or without making intermediate drawings from which the axonometric drawing can then be made. Understandably, reorienting the views or making intermediate drawings increases the number of steps required to produce the resulting axonometric view, as compared to directly producing the axonometric view directly from the orthographic views.
One problem in providing an axonometric view of an object represented in two orthographic views is that of drawing representations of circles or arcs of circles in the axonometric view. Standard ellipse templets are useful for drawing representations of circles or arcs or circles, but the standard ellipse templets are typically available in five degree multiples and therefore are not always appropriate for drawing representations of circles or arcs of circles in the axonometric views unless the surfaces of the axonometric view upon which the circles or arcs of circles are to be represented are oriented at multiples of five degrees to non-converging lines or sight normal to the viewing plane of the axonometric view.